Regulation of the cytoskeleton and cell migration is an important aspect of cancer invasion and metastasis. This project focuses on a novel protein, Nischarin that has an inhibitory role in cell migration and invasion. Integrins have been implicated in cellular processes including the organization of actin cytoskeleton, cell growth and survival, cell motility and cell invasion. We have identified a novel protein that specifically interacts with the a5 cytoplasmic tail;we have termed this protein 'Nischarin'. Recently, with the help of effector domain mutants of Rac1, we demonstrated that Nischarin selectively inhibits Rac-driven signaling cascades that act through p21 activated kinase (PAK). These observations suggest that Nischarin affects the process of cytoskeletal regulation mediated by Rac and PAK. Consistent with this, Nischarin binds to PAK, and inhibits the kinase activity of PAK. Furthermore, our recent data indicate that Nischarin siRNA stimulates lamellipodia formation and cell migration, and activates PAK kinase, suggesting that Nischarin is an important regulator of cell motility. The intent of the proposal is to investigate further the newly described biochemical connection between PAK and Nischarin and its role in tumor cell migration and invasion. In Aim I we will address the role of Nischarin in the migration and invasion of carcinoma cells by over or underexpressing Nischarin. Also we will examine spatio-temporal localization and regulation of PAK and Nischarin in pseudopodia and invadopodia. In Aim II, we will study the effect of Nischarin on downstream effectors of PAK including LIMK and cofilin, and will examine how this affects invasion of cancer cells. In Aim we will evaluate Nischarin's effects on lamellipodia formation by studying lamellipodial dynamics with live cell imaging;we will visualize the effects on lamellipodial protrusion, lamellipodial retraction and membrane ruffles. Evaluation of the role of Nischarin and PAK in the regulation of tumor cell migration and invasion will broaden the current understanding of PAK signaling in carcinoma cells, and may provide new avenues for therapeutic intervention.